A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head, which is housed in a slider, and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies in part on a suspension's force on the slider and on the aerodynamic characteristics of the slider air bearing surface (ABS) to provide the proper distance between the read/write head and the surface of the magnetic-recording disk (the “flying height”) while the magnetic-recording disk rotates. A slider therefore is said to “fly” over the surface of the magnetic-recording disk.
Resistor temperature detector (RTD) systems have been used in the prior art to determine when the slider head makes physical contact with the magnetic-recording disk based upon the temperature of an element, such as an embedded contact sensor (ECS), embedded in the slider near the read/write head. ECS elements sense physical contact of the slider with the disk based on the ECS element's resistance, e.g., the amount of voltage across the element, which is affected by the temperature change caused by such physical contact.
Thermal flying height control (TFC) systems have been used in the prior art to fly the read/write head as close as possible to the magnetic-recording disk for effective operation of the head. Typically, TFC systems gently urge the head area of the slider toward the disk until contact is made (“touchdown”) at which point the slider is urged away from the disk (“pull-back”). Touchdown and pull-back are effectuated by, respectively, providing electrical current to a heater element which causes the surrounding slider materials to expand and therefore protrude outward closer to the disk and then slightly reducing the current to the heater element to cause the surrounding slider materials to consequently contract away from the direction of the disk. In HDD systems having an ECS, the ECS is often used to sense the touchdown event, as described.
However, in prior art approaches no mechanism for flying height sensing during the HDD lifetime is used, but only pre-calculated corrections to the TFC settings are applied due to temperature or pressure changes.